1.Field of the Invention
The present invention relates in general to the gasification of fuels comprising solid components.
More particularly, the invention relates to a device for converting a fuel comprising solid components, known as a solid fuel, into a gaseous fuel, said device comprising:                a pyrolysis zone for the pyrolyzing solid fuel, comprising pyrolysis means that are capable of decomposing said solid fuel into a pyrolysis gas and into a solid pyrolysis residue, known as coke; and        
2. Description of the Related Art                a combustion zone, which is distinct from the pyrolysis zone, for burning said pyrolysis gas and comprising combustion means.        
Said gaseous fuel obtained with the aid of such a device is an energetic gas, generally termed syngas, which can be used to drive appropriate equipment such as engines, turbines, or even fuel cells. However, syngas often contains tars, and equipment suitable for being supplied with syngas has a low threshold of tolerance to tar. Beyond a corresponding tolerance threshold, condensation of tar in such equipment causes rapid deterioration of said equipment.
Specific gas treatment units exist that can be used to reduce the quantity of tar remaining in the syngas. However, such treatment units are bulky and expensive.
Devices known as staged gasification devices are known in the art; they comprise a pyrolysis zone and a distinct combustion zone. The gasifier from the Danish manufacturer TK Energi AS is an example. A device of that type can be used to reduce the tar content in the syngas obtained because the pyrolysis and combustion steps are partially separated out.
However, in such a known prior art device, a portion of the solid fuel is burned in order to provide the heat necessary for pyrolysis. Direct combustion of a solid of that type results in a loss of the energy efficiency of the device, as well as in the emission of polluting gases, for example dioxins.
Further, said pyrolysis and combustion zones are arranged for positioning end-to-end, and so the coke obtained from pyrolysis of the fuel passes through the combustion zone in order to form a reduction bed in the reduction zone, which means that the device becomes very bulky and the risk of polluting emissions is increased. Finally, the arrangement of the pyrolysis and combustion zones in such devices causes large energy losses in the combustion zone, which is not beneficial to the pyrolysis zone.
US2009/282738 discloses a device for converting a solid fuel into a gaseous fuel, which device comprises a pyrolysis zone and a combustion zone provided with combustion means.
However, in the device of document US2009/282738, the solid fuel is burned in the combustion zone and the combustion gases then circulate in the pyrolysis zone.
Thus, the device of that document US2009/282738 generates the same problem as that proposed by the Danish manufacturer TK Energi AS, which burns solid fuel to add energy. Such combustion of solid fuel generates polluting emissions and leads to a loss of energy efficiency.
Further, the solution in that document US2009/282738 is not aimed at obtaining an energetic gas, but rather a pyrolysis oil. It is then necessary to burn solid fuel in the combustion zone throughout the operation of the device in order to provide the additional heat required to carry out the pyrolysis reaction.
Document WO02/40618 A1 describes a device comprising a central pyrolysis zone surrounded by a combustion zone. Such a configuration can be used to transmit part of the heat obtained from combustion to the pyrolysis zone, but large losses of heat have been observed from the combustion zone to the outside of the device. Thus, heat recovery by the pyrolysis zone is not optimized.
The aim of the present invention is to propose a device for converting a solid fuel into a gaseous fuel that can be used to limit heat losses from the combustion zone out of the device and to improve heat recovery by the pyrolysis zone.